<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8" />
		<title></title>
		<script>
			
			var a='name:"jack"';
			
			var b='{name:"jack",age:"15"}';
			
			var c='[{"name":"jack","age":"15"},{"name":"tony","age":"25"}]';
			
			console.log(a.substr(0,3))
			console.log(a.substring(0,3))
			
			console.log(b.length)
			console.log(b.concat('456'))
			console.log(b.substr(3))
			
			console.log(c.length)
			console.log(c.concat('456'))
			console.log(c.substr(3))
			
			var bb=JSON.parse(c);
			
			console.log(bb[0].name)
			
		</script>
	</head>
	<body>
		
	</body>
</html>
